The present invention is directed to an electric discharge lamp with an inner and an outer jacket and, more specifically, to a high intensity discharge (HID) lamp that has two generally concentric jackets.
Modern metal halide sealing technology and the advent of ceramic lamp envelopes have led to development of a new class of metal halide lamps, such as described in U.S. Pat. No. 5,424,609 and in J. Ill. Eng. Soc. P 139-145, Winter 1996 (Proc. of IESNA Annual Conference). These lamps contain metal halide fill chemistries and two electrodes, and rely on the application of a high voltage pulse between the electrodes to ignite the lamp. Normal current and voltage are then applied through the two electrodes. The gases within the vessel are excited into a plasma state by the passing of electric current. Typical chemical fills include scandium and rare earth halides with various other additives including thallium halide and calcium halides, in addition to a starting inert gas such as argon or xenon.
The arc tube, in which the plasma is contained, also called a burner, is often jacketed within another envelope, called the outer jacket, to protect it from the air. Many of the lamp parts, especially niobium electrical inleads, can oxidize rapidly at operating temperatures and cause the lamp to fail. These outer jackets are usually well removed from the burner and filled with an inert gas and a getter material, for example a zirconium-aluminum compound, to getter oxygen and hydrogen. While the outer jacket is in thermal contact with the burner, the contact is limited so the outer jacket can operate at substantially lower temperatures, for example about 200xc2x0 C. compared to the burner at 900xc2x0 C. One such double jacketed lamp is described in U.S. Pat. No. 4,949,003 and another is described in U.S. Pat. No. 6,316,875.
Lamps have been made with a vitreous silica envelope that contain chemistries other than metal salts, such as sulfur, tellurium and selenium as described in U.S. Pat. No. 5,404,076. These lamps are powered by microwaves and can be quite efficient, for example 130 lumens/Wrf, but have never successfully penetrated the market because of power supply inefficiencies and the generally large lumen output for 1 kW lamps ( greater than 130,000 lm). The difficulties in operating these lamps in an electroded manner, at wattages less than a kilowatt, is the rapid and violent attack on the electrodes by the chemical fill. For example, tungsten electrodes react in the presence of hot sulfur vapor to form tungsten sulfide, which vaporizes, and lamp operation ceases. Elaborate schemes for using these chemical fills with protected electrodes have been discussed in the literature, but have not materialized in the marketplace, for example U.S. Pat. No. 5,757,130 and U.S. Pat. No. 6,316,875.
There is great interest in improving the efficacy of high intensity discharge (HID) lamps for environmental reasons and for introduction of HID lamps into residential markets. Improving the HID lamp efficacy should translate into lower wattage lamps (less power) operating on low wattage (less expensive) electronic ballasts in homes, similar to compact fluorescent systems, while providing more visible light. In addition, for higher wattage HID lamps, should result in lower utility bills for cities and towns and industrial installations without sacrificing safety or illumination levels.
Accordingly, an object of the present invention is to provide a double jacketed HID lamp that has a greater visible light output than the conventional double jacketed HID lamp.
A further object of the present invention is to provide a electric discharge lamp that has a double jacketed bulb with a sealed inner chamber containing a first material that emits light when activated and a separately sealed outer chamber between the double jackets, where the outer chamber contains a second fill material that converts light outside the visible spectrum that has been emitted from the inner chamber to light in the visible spectrum, which is emitted from the outer chamber, to thereby increase an amount of visible light generated by the lamp.
A yet further object of the present invention is to provide such a lamp where the second fill material in the outer chamber is vaporizable by heat from the inner chamber during operation of the lamp.
Another object of the present invention is to provide such a lamp where the second fill material in the outer chamber converts ultraviolet and deep blue light from the inner chamber to light in the visible spectrum.
Yet another object of the present invention is to provide such a lamp where the second fill material is one of sulfur, selenium, and tellurium.
Still another object of the present invention is to provide a method of increasing an amount of visible light from a double jacketed lamp that includes the step of providing a material in the outer chamber that, when vaporized by heat from the inner chamber when the lamp is operating, converts ultraviolet (UV) light emitted from the inner chamber to a visible light, thereby increasing an amount of visible light transmitted through the outer jacket from an amount of visible light transmitted through the inner jacket.